تخمین بار برف و یخ جهت طراحی خطوط انتقال نیرو فشار قوی با دوره‌های بازگشت چند ساله (مطالعه موردی: ارتفاعات غربی مازندران)

یکی از مشکلات شرکت برق منطقه‌ای در مناطق سردسیر، یخ‌زدگی و نشست برف بر روی سیم‌های خطوط انتقال نیرو می‌باشد. پهنه‌بندی آب و هوایی و ارائه شرایط بارگذاری متناسب با منطقه جهت طراحی مکانیکی خطوط حائز اهمیت بوده و انتخاب صحیح این شرایط به‌لحاظ فنی و اقتصادی تاثیر بسزایی در طراحی پروژه خواهد داشت. نقشه بار برف و یخ که در گذشته توسط وزارت نیرو تدوین گردیده، کارایی و نوآوری لازم را نداشته و یا اینکه برای بسیاری از مناطق توسعه یافته جدید شهری و روستایی بازنگری نشده است در این تحقیق پارامتر آماری ضخامت یخ با دوره‌های بازگشت چند ساله، که ازجمله بارهای موثر در بارگذاری دکل انتقال نیرو هستند با استفاده از داده‌های هواشناسی (سال 2010 تا 2018 میلادی) سه ایستگاه کوهستانی بلده، کجور و سیاه بیشه در غرب مازندران مورد ارزیابی قرار گرفتند و در نهایت مقادیر اسمی جدید با دوره بازگشت‌های مختلف پیشنهاد گردیده است. نتایج نشان داد که برای طراحی خطوط انتقال نیرو با دوره بازگشت کمتر از 50 سال، منطقه بلده و کجور جزو مناطق سنگین و با دوره بازگشت بیشتر از 50 سال جزو مناطق فوق سنگین و منطقه کجور با دوره بازگشت 50 تا 100 ساله جزو مناطق متوسط و دوره بازگشت بیشتر از 100 سال جزو مناطق سنگین (مطابق با آیین نامه مشانیر) می‌باشد.

Estimation of snow and ice accretion for the design of high-pressure transmission lines with multi-year return periods (case study: western highlands of Mazandaran)

IntroductionOne of the problems of the power companies in cold areas is freezing and snowfall on the transmission lines. Therefore climatic zoning of the Mazandaran province and the load conditions in accordance with requirements of the region are important for the mechanical design of the transmission lines. The correct selection of these conditions have a significant technical and economic impact on designing the project. One of the problems of a regional power company in cold, frosty and snowy areas is the wiring and shielding of power lines. Snow and ice load maps developed by the Ministry of Energy do not have the necessary efficiency and innovation anymore and were not reviewed for many newly developed urban and rural areas. Iran is divided into four regions of light, medium, heavy and super heavy in terms of weather conditions and for each of these regions, the four main and primary variables of loading, namely normal wind speed, maximum wind speed, normal ice thickness and maximum ice thickness are provided.Materials and MethodsThe purpose of this study is applied and the nature and method of research is descriptiveanalytical. In this study, the parameter of ice thickness with multiyear return periods, which is one of the effective loads in the loading of the power transmission lines, was evaluated using the weather data (2010 to 2018), at three mountain stations of Baladeh, Kajur and Siah Bisheh in western Mazandaran. Meteorological information is measured hourly at meteorological stations, After collecting and correcting the meteorological data, in the Excel environment and in the final worksheet, the program is written to calculate the daily, monthly, and annual ice thicknesses and to calculate the statistical parameters at a height of 35 meter (mean height of the cables). Using the Smada software, the relevant histograms are plotted.Results and Discussion Eventually, new nominal values were recommended with different return periods. The results showed that in the design of transmission lines with a return period of less than 50 years, Baladeh and Kojur regions are among the heavy areas. With a return period of more than 50 years these points are considered as superheavy. With the return period of 50 to 100 years, the Kojur area is an intermediate region and a heavy region with the return period of>100 years (in accordance with the Ministerial code also known as Mashanir Code). Therefore calculated values of snow and ice loads for 10 m (less than 66 kW) and 35 m (above 220 kW) elevations were not significant, Based on the results, it is suggested that with the establishment of automatic weather stations in the area and field and laboratory studies, more detailed results will be obtained in future studies.ConclusionIn this research, the ice thickness statistical parameters with multiyear return periods were evaluated, using meteorological data and simulation methods. The meteorological data was provided by Mountain Engineering Laboratory and Research Institute. Finally new nominal values were suggested after comparing them with various return periods. In the case of Baladeh, calculated values of snow load and ice for a height of 35 meters, with different return periods from 50 years onwards, the maximum amount of ice exceeds the nominal value (40) and was likely to cause damage to transmission lines. Therefore, for the design of power lines with a return period of less than 50 years, Baladeh region is one of the heavy areas and with a return period of more than 50 years, it is one of the super heavy areas.For the Siahbisheh area, the amount of snow and ice for the 50 to 100year return period is moderate, and for return periods greater than 100 years, the heavy areas are less than the nominal average value defined in the Ministerial code(Mashanir). In the Kojour area, which according to Mashanir is a superheavey region, for return periods from 50 years onwards the maximum amount of ice thickness exceeds the Mashanir code. Therefore the probability that it could damage the transmission lines is greater than the nominal value (40). Hence, for the design of power lines with a return period of less than 50 years, the Kojour region is a heavy area and with a return period of more than 50 years, it is a heavy area.